The development of microporous foams has been the subject of substantial commercial interest. Such foams have found utility in various applications, such as thermal, acoustic, electrical, and mechanical (e.g., for cushioning) insulators, absorbent materials, filters, membranes, carriers for inks, dyes, lubricants, and lotions, making items buoyant, and the like. References describing such uses and properties of foams include Oertel, G. "Polyurethane Handbook" Hanser Publishers, Munich, 1985, and Gibson, L. J.; Ashby, M. F. "Cellular Solids Structure and Properties" Pergamon Press, Oxford, 1988. The term "insulator" refers to any material which reduces the transfer of energy from one location to another. The term "absorbent" refers to materials which imbide and hold or distribute fluids, usually liquids, an example being a sponge. The term "filter" refers to materials which pass a fluid, either gas or liquid, while retaining impurities within the material by size exclusion. Other uses for foams are generally obvious to one skilled in the art.
For many uses, composite and generally conflicting requirements are placed on the foam itself. These may include (1) low density, (2) flexibility, (3) strength (compressive and tensile), (4) openness, and (5) control of morphology. Low density foams are more efficient since most uses require a certain volume and a low density foam will impose less mass to meet this objective. Flexible foams are typically generated by maintaining a relatively low glass transition temperature ("Tg") of the foam. Strength is a parameter which is inevitably sacrificed to achieve either lower Tg or lower density. Strength can be generated effectively by including crosslinking agents which link the polymeric chains of the foam together in a fashion which confers a degree of resistance to deformation and the ability to recover from deformation, e.g., elasticity. Openness and morphology are controlled principally by the method of foam formation and curing.
Accordingly, it would be desirable to be able to make an open-celled, high surface area polymeric foam material that: (1) has the lowest density consistent with the other requirements imposed on the foam; (2) is flexible; (3) is strong; (4) has a generally open-celled structure; and (5) can be manufactured so as to control the size of cells produced within the foam.